(i) Field which invention relates to
The present invention is with respect to a three-roller universal joint with a system for positive guiding of the three rollers used for the torque or driving force, in the case of which for causing the radial change in position of the rollers in relation to the male, inner part of the joint, use is made of spherical running or controlling faces on the rollers, which by way of a controlling part, placed in the middle of the joint and acting on all three rollers at the same time, are each kept against an opposite controlling or running face of the outer or female joint part, such opposite controlling faces being positioned in each case at the floor of one of three grooves, parallel to the axis of turning of the joint, for the three rollers transmitting the driving force.
(ii) The prior art
In the first design of such a three-roller universal joint, see U.S. Pat. No. 2,910,845, use was only made of centrifugal force for keeping the three torque-transmitting rollers, which have a spherical face, against the floors of the grooves in which they are placed, such centrifugal force further controlling radial motion of such rollers in relation to the inner or male joint half.
The first positive controlling or confining system for the three rollers of such a joint was set forth in French Pat. No. 1,272,530, which is generally based on the idea of having the grooves of the outer or female joint half, and which take up the three driving rollers, designed so as to be placed round the spherical faces of the rollers, on the two sides of their turnpins, so as to give a cage-like structure making certain of positive control and guiding of the rollers' radial motion in relation to the male inner or core joint half.
A positive guiding system for the three rollers or balls of a three-unit joint using a driving part placed in the middle of the joint for acting on all three rollers or balls at the same time is to be seen in German Auslegeschrift specification No. 2,225,499, this patent marking the start of a line of development which was responsible for a number of patent applications for positive guiding or controlling systems with a controlling part placed in the middle of the joint. German Offenlegungsschrift specification No. 2,355,765 may be noted in this respect as representative of this branch of development in the universal joint art.
To give a balanced account of the prior art, German Offenlegungsschrift specification No. 2,216,345 is lastly to be noted whose three-unit universal joint has a middle, floatingly positioned ring part acting on the three rollers, used for torque-transmission, at the same time by way of a flat running face. However, in the case of this prior art design it is not a question of a positive controlling or confining system, because in this case the ring part or annulus is not able to be a stiff or rigid body, and in fact has to be a giving spring structure, able to undergo a change in form and having a low springing force.
All three roller or three ball universal joints, in some cases named "tripod joints", have the design-based shortcoming of a great size of the motion of the three torque-transmitting rollers in relation to the inner or male joint half because, when the two joint halves are not in time, the rollers or the like have to be moved radially between two limits of motion on each turn of the joint structure. At one of these limits of motion or extreme positions the roller comes nearer to the inner or core joint half by a certain degree, while in the other limit of its motion it is moved by three times this amount away from the middle of the joint. These amounts of motion are roughly equal to the square of the angle by which the joint halves are out of line. In the case of a three-roller joint, designed for an upper limit of the rated torque of 150 mkp, there will be a motion of about 3 mm radially outwards of each roller even when the joint halves are only 20.degree. out of line, that is to say when the two shafts are angulated by 20.degree.. Because three-roller joints are mostly used for universal joint shafts for driving the wheels of motor vehicles, and because in the case of front wheel driving system the joint halves may be up to 47.degree. out of line, in the case of present-day designs relative motions of up to 15 mm may be produced. Three-roller universal joints have however furthermore so far the design-based shortcoming that, when the two halves are running out of line, the middle of the inner joint half is eccentrically moved out of position in relation to the middle of the outer or female joint half, and because of the oscillating motion produced there will be a further increase in the noise and out-of-balance condition, which in any case will be caused by the radial motion of the three rollers.